The present invention relates to character recognition systems and, more particularly, to character position detectors for use in character recognition.
In character recognition systems the document to be read is located in a reading station by means of a document transport. At the reading station the difference in reflectance between a character and the document background is detected optically and is converted into an electrical signal that is stored in a memory. Typically this conversion is done a line at a time and the data is stored in a line memory. Once in the line memory the data can be searched to locate the character margin or perimeter and processed (e.g. thinned and scaled) as shown in U.S. Pat. No. 3,541,511 issued to Genchi et al. Then the data is transferred to a classifier memory where the character is identified, e.g. by comparing the data to character masks such as is explained in U.S. Pat. No. 3,766,520 issued to Patterson.
The typical position detector is a program in the system controller or processor. This program checks the memory locations in some pattern, searching for black/white or white/black transitions that indicate either the perimeter of the character or at least the left, right, top and bottom margins of the character. Essentially the position detector program requests a word, from the line memory over the controller's operating or B-bus. Once in the controller's internal memory, the data is compared to see whether it is the same as the previously selected data bit in the series, i.e. is it a transition bit. If the bit is a transition bit its position is recorded at the controller's memory and the next bit is brought to the controller from the line memory. After the search sequence is completed the address of the transition bits that are leftmost, rightmost, uppermost and lowermost are used as the margin of the character.
During the period when the position search is going on the system controller and the B-bus are occupied and cannot perform other functions, such as reading new data at the read station or transferring character fields, i.e. the data within the margins located by the position program, to the character memory for identification. Also, the operation of a programmed search is inherently much slower than a hardware implemented search. Therefore an improvement in character recognition systems could be achieved if the character position detection were carried out independent of the system controller and B-bus by a hardware device.